1. Field of the Invention
The invention pertains generally to devices for pneumatic atomization of liquids to provide atomized liquid spray jets and, more particularly, to a paint sprayer gun nozzle providing a flat spray jet.
2. Discussion of the Related Art
In the art of pneumatic paint spray guns, a liquid to be atomized, generally paint, is supplied to a nozzle nearly underpressurized. Atomizing air is supplied under pressure to an annular gap concentrically surrounding an exit aperture of the nozzle. The liquid emerging from the nozzle aperture is atomized by the pressurized atomizing air streaming from the annular gap.
Due to the shape of the annular gap, the atomized liquid is emitted from the nozzle in the form of a conically expanding spray jet. However, frequently, a flat, fan-shaped spray jet is desired.
In one attempted solution for providing a fan-shaped spray jet, a paint spray gun spray nozzle is provided with two air exit bores or openings, so-called air horns, at opposite sides in front of the nozzle. The air horns are orientated diagonally relative to the nozzle axis to direct air horn jets at a forward slanted direction to thereby compress the conically expanding spray jet to form a flat fan-shaped spray jet. The production of the flat edged spray jet is due to the natural line produced by two intersecting cones; the spray jet and the air horn jet. However, a uniformly flat or planar fan-shaped spray jet is not always produced. Instead, a cross-section of the fan-shaped spray jet includes a thin middle ridge and spreading end regions, i.e. there is a lower concentration of liquid or paint in the middle region than at the end regions.
In another attempted solution, air horns in a sprayer device are provided with a plurality of air exit bores or openings to improve the uniformity of the fan jet. However, this solution has not been entirely successful because the fan-shaped jet produced has a wavy cross-section.
In yet another attempted solution to provide a flat, fan-shaped spray jet, a paint sprayer is provided with limiter air jets which are produced by air exit bores or openings located at opposite sides of the sprayer nozzle or the annular gap for atomizer air. Essentially, the air exit bores or openings direct air jets parallel to the nozzle axis and onto the concially expanding spray jet. The limiter air jets strike the conically expanding spray jet in front of the air horn jets to deform the conically expanding spray jet so that it has an oval cross-section. However, not only is a completely planar fan-shaped spray jet not produced in this attempted solution, the limiter air bores or openings located adjacent to the annular atomizer air gap are generally connected to the atomizer air source. The sole sourcing of atomizer air and limiter air permits only a single optimum operating point which depends upon the degree of atomization desired and does not include means for compensating for the thickness of the fan-shaped spray jet as determined by the air horns, which are usually controlled separately.
Providing a paint sprayer with a plurality with superfine air horn bores and/or limiter air bores involves difficulties in terms of production engineering and entails a risk of blockage due to contamination. Furthermore, while the foregoing discussion is predominantly true for sprayer devices utilizing pneumatic atomization exclusively, it is also true to a degree for devices utilizing combined pneumatic-hydrostatic methods including a hydrostatic middle pressure, a slotted nozzle, and additional compressed air.